JPS6285579A - Driving method for solid-state image pickup device - Google Patents

Abstract

PURPOSE:To suppress blooming and highlight afterimages by applying a stored excess charge to a pulse voltage in synchronizing with a signal charge reading pulse and making said excess charge flow to a charge control electrode. CONSTITUTION:When the intensive light is made incident on a photoconductive film 21, the produced signal charge is stored in a charge storing diode 12 of a storing part up to the maximum level prescribed by the voltage applied to a charge control electrode 17. This stored signal charge is read outside via a transfer part in response to a signal reading pulse. Here a pulse in synchronizing with the signal reading pulse is applied to the electrode 17 and the amount of the stored charge of the diode 12 is reduced. Then the stored charge partially flows out to the electrode 17 and the charge scarcely remains at the diode 12 and the transfer part after the charge is transferred. As a result, the blooming and the highlight afterimages are suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for driving a solid-state imaging device in which photoconductive films are stacked.

[Technical background of the invention and its problems]

Solid-state imaging devices that perform photoelectric conversion using a photoconductive film have high sensitivity because they have a large aperture ratio. Furthermore, since most of the amount of incident light is absorbed within the photoconductive film, less charge is generated within the Si substrate, resulting in low smear. Furthermore, the spectral sensitivity can be freely selected depending on the type of photoconductive film, so recently,
Amorphous silicon film y Zr1l-x CdzTe
Development of solid-state imaging devices with laminated films, etc. is progressing.

An example of this type of solid-state imaging device is one in which a photoconductive film and a transparent electrode are sequentially laminated on a semiconductor substrate having a charge transfer function, such as a CCD. That is, a pixel electrode connected to a diode region formed on the semiconductor substrate and separated for each pixel is provided on the semiconductor substrate, a photoconductive film is formed on the pixel electrode, and a transparent electrode is further formed on the photoconductive film. It is set up. Note that in order to smooth the surface on which the photoconductive film is formed, an insulating layer made of an organic or inorganic insulator may be formed on the uneven surface of the semiconductor substrate.

Incidentally, in this solid-state imaging device, the capacitance of the photoconductive film is often larger than the capacitance of the charge transfer section.

Therefore, when strong light is incident, the generated signal charges that exceed the maximum amount of charge that can be transferred by the charge transfer section overflow as excess charges at the charge transfer section or are left unread in the storage section. . This causes phenomena called blooming and highlight afterimages.

This will have a negative effect on image quality.

In order to solve this problem, for example, the solid-state imaging device proposed in Japanese Patent Application Laid-Open No. 59-270688,
A charge control electrode is provided in ohmic contact with the photoconductive film at a position corresponding to the gap between the pixel electrodes. If the signal charge is an electron, for example, by applying a voltage higher than the potential of the pixel electrode when excess charge begins to be generated in the photoconductive film to the charge control electrode, the excessively generated charge can be removed from the charge control electrode. leak. In this way, blooming and highlight afterimages are suppressed.

However, since a DC voltage is applied to the charge control electrode, the above-mentioned effect occurs during the period when signal charges are being accumulated, but during the period when signal charges are being read from the storage section to the charge transfer section, the accumulation does not occur. Since the potential of the charge control electrode is higher than that of the charge control electrode, the charge generated by the incident light during this period cannot flow to the charge control electrode and is accumulated in the charge transfer section and the storage section. I end up. As a result,
Charges generated during a period in which signal charges are read from the storage section to the charge transfer section are left behind in the charge transfer section and the storage section, causing blooming and highlight 1 to afterimages to occur.

[Object of the Invention] The present invention has been made to solve these conventional drawbacks, and provides a driving method for a solid-state imaging device that can completely remove generated excess charge and suppress blooming and highlight afterimages. The purpose is to provide a method.

[Summary of the invention]

That is, in the present invention, after signal charges generated in a photoconductive film that performs photoelectric conversion are accumulated in an accumulation section, the amount of signal charges is controlled by a charge control electrode electrically connected to the photoconductive film, and the signal charges are transferred in a charge transfer section. Regarding a method of driving a solid-state imaging device formed by transferring, a pulse voltage is applied to a charge control electrode in synchronization with a signal readout pulse for reading out signal charges from an accumulation section to a charge transfer section;
The feature is that the excess charge accumulated in the accumulation section is flushed out to the charge control electrode.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to the drawings.

FIG. 3 is a diagram showing an example of a solid-state imaging device to which the present invention is applied. In the figure, the photoelectric conversion section (2) includes a photoconductive film made of hydrogenated amorphous silicon or the like, and a transparent electrode, such as ITO, formed on the photoconductive film. Further, a pixel electrode (2) made of metal forming a pixel is electrically connected to the storage section (2), and signal charges generated in the photoelectric conversion section (2) are accumulated in the storage section (2). The vertical charge transfer section () is adjacent to the storage section (2), and the accumulated signal charges are transferred to the horizontal charge transfer section (C) via the vertical charge transfer section (). Further, this signal charge reaches the video signal output section 0 connected to the horizontal charge transfer section (2) and is taken out as a video signal.

FIG. 4 is a cross-sectional view of a pixel of the solid-state imaging device shown in FIG. 3. In the figure, on one surface of a semiconductor substrate (10), for example, a P-type silicon substrate, there is an n÷-type buried channel CC.
A vertical C (11) consisting of D and a charge storage diode (I2) consisting of a pn junction are formed adjacent to each other.An insulating film (14) for insulating the transfer electrode (13) is The charge storage diode (12) is formed together with the transfer electrode (13) so that a part of the n-type region is exposed.In this way, a storage section and a charge transfer section are formed in the semiconductor substrate (10). .

Note that a predetermined pulse is applied to the transfer electrode (13) from the outside, and by applying a charge readout pulse to the transfer electrode (13), the charge storage diode (
After the charges in 12) are transferred to the vertical COD (11), they can be sequentially transferred in one direction. A first electrode (15) made of, for example, aluminum is placed on the semiconductor substrate (lO) so that a part of the electrode is in contact with the charge storage diode (12), that is, the storage part.
) are formed separately from each other.

Further, an insulating layer (6) made of polyimide, for example, is formed on the first electrode (15) to smooth it. The formation of this insulating layer (16) is carried out twice; first, after smoothing the uneven surface of the semiconductor substrate (10) in the first formation, a charge control electrode (17) made of aluminum, for example, is formed; Furthermore, by performing the second formation, the charge control electrode (17) is embedded in the insulating layer (16). Note that the charge control electrode (17
) is formed at a position corresponding to the gap between the pixel electrodes (18), which will be described later, and is connected to an external power source (
19). Contact holes (20) are provided in the insulating layer (16), and pixel electrodes (18) made of, for example, aluminum are formed on the insulating layer (16) at predetermined intervals. Note that the pixel electrode (18) is electrically connected to the first electrode (15) via a contact hole (20). Also, a part of the insulating layer (16) on the charge control electrode (17) is removed.

Only the ends become embedded in the insulating layer (16). Then, the pixel electrode (18) and the exposed charge control electrode (
17) On top of the photoconductive film (21), for example, i-type hydrogenated amorphous silicon, a barrier layer (22), for example, p-type hydrogenated amorphous silicon carbide, and a transparent electrode (23), for example, made of ITO. The charge control electrode (17) is formed in sequence and is electrically connected to the photoconductive film (21).

Here, the barrier layer (22) has the function of blocking charge injection from the transparent electrode (23). Also, transparent electrode (
23) is connected to an external power source (24) in order to apply a bias voltage to the photoconductive film (21).

Next, one embodiment of the present invention will be described using FIGS. 1 and 2. Here, FIG. 1 shows the transfer electrode (13
) and the pulse waveform applied to the charge control electrode (17), the figure (,) is the pulse timing applied to the transfer electrode (13), and the figure (b) is the pulse waveform applied to the charge control electrode (17). Figures 2(a) to (4)) represent the pulse timings for periods 11 to 11 in Figure 1, respectively.
FIG. 4 is a diagram showing changes in the potentials under the storage section, the charge transfer section, and the transfer electrode (13) at t.

In FIG. 1(a), A is a transfer pulse, B is a signal read pulse, and period 1. ．． At step 13, signal charges are read from the storage section to the charge transfer section. Moreover, as can be seen from FIG. 1(b), the pulse voltage synchronized with the signal readout pulse B, that is, the maximum amount of signal charge that can normally be transferred by the charge transfer section, is accumulated in the charge control electrode (17). The voltage vC1 corresponding to the potential of the storage section is, for example, 2V, but during the period t3tt4, a pulse voltage of 4V, for example, is applied to the voltage Vc corresponding to the potential of the storage section in a state where no signal charge is stored.

In the solid-state imaging device shown in FIGS. 3 and 4, strong light is applied to the photoconductive film (21) that performs photoelectric conversion through the iode (
12) That is, the charge is accumulated in the accumulation section, but as shown in FIG. 2(a), a voltage Vc is applied to the charge control electrode (17) electrically connected to the photoconductive film (21). Therefore, the potential of the storage section is defined by the potential vc1 even if there is intense radiation, and the storage section has the maximum amount of charge Q7 that can be transferred by the charge transfer section.
max is accumulated. Next, for example, a period t of 25 μSeC
At 2, the signal read pulse B is turned ON, so that the charge Q7max is transferred to the charge transfer section. However, at this time, as the charge Q7max flows out to the charge transfer section,
Since the potential of the storage section rises and the voltage Ve becomes higher,
Charge Qa generated by excessive light during this period 1 s is accumulated in the charge transfer section and the accumulation section as shown in FIG. 2(b), and the potential of the accumulation section is lowered to voltage Vc. The charge Qa accumulated in this state becomes an excess charge and cannot be transferred completely by the charge transfer section. Therefore, by applying the voltage Vc to the charge control electrode (17) during a period t1 of, for example, 25 μsec, the charge QB flows to the charge control electrode (17) with a higher potential and disappears, as shown in FIG. 2(c). .

That is, the potential of the storage section is defined by Vc, and the maximum transfer charge amount (17max) remains in the charge transfer section.Next, for example, during a period t4 of 25 μsec, the signal read pulse B is turned off and the charge Q7max remains. transfer has started.

By applying a pulse voltage synchronized with the output pulse, it is possible not only to control the amount of signal charge accumulated in the storage section within a range that can be transferred by the charge transfer section, but also to control the amount of signal charge that can be transferred from the storage section. It is possible to remove even the excess charge generated during the period of readout to the memory cell. As a result, it is possible to suppress blooming caused by excess charges overflowing in the charge transfer section and highlight afterimages caused by charges left behind in the accumulation section.

〔Effect of the invention〕

As explained above, in the driving method of the solid-state imaging device of the present invention, by applying a pulse synchronized with the signal readout pulse to the charge control electrode, excess charge generated during the signal readout period can be removed, and strong incident light can be removed. Good images with no blooming or highlight afterimages can be obtained even when

[Brief explanation of drawings]

FIG. 1 is a diagram showing pulse waveforms applied to a transfer electrode and a charge control electrode in an embodiment of the present invention, and FIG. 2 is a diagram illustrating changes in potential of an accumulation section and a charge transfer section in an embodiment of the present invention. , FIG. 3 is a configuration diagram showing an example of a solid-state imaging device to which the present invention is applied, and FIG. 4 is a pixel sectional view of the solid-state imaging device shown in FIG. 3. (11) Vertical CCD (12) Charge storage diode (13) Transfer electrode (17) Charge control electrode (21) Photoconductive film (23) Transparent Electrode agent Patent attorney Norio Ken Chika Yudo Norio Ogo Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] A photoconductive film that performs photoelectric conversion, a transparent electrode formed on this photoconductive film, an accumulation section that accumulates signal charges generated in the photoconductive film, and a storage section that transfers the signal charges accumulated in this accumulation section. In a method for driving a solid-state imaging device comprising a charge transfer section and a charge control electrode electrically connected to the photoconductive film and controlling the amount of charge in the photoconductive film, the charge transfer section is moved from the storage section to the charge transfer section. A method for driving a solid-state imaging device, characterized in that a pulse voltage synchronized with a signal read pulse for reading out the signal charge is applied to the charge control electrode.